1. Field of the Invention
The present invention is directed to a video camera and method for simulating the broadcast look of motion picture film. More specifically, the invention provides a video camera design and method for real time digital video simulation of motion picture film.
2. Description of the Prior Art
Television broadcasts generally can be thought of as providing two distinctly different "looks." Viewers of television broadcasts can commonly discern a difference between the look of a broadcast from a video camera and the look of the broadcast from motion picture film. For example, the news, game shows and afternoon soap operas are typically shot on video cameras whose signals are recorded on videotape. In contrast, broadcasts of programming that originated on motion picture film are often thought of as presenting a different and richer "look" than that of a video camera broadcast.
Motion picture film is commonly transferred to videotape for editing and broadcast purposes. However, even under such circumstances the motion picture film retains the unique richer film "look." This richer look is associated with the higher quality, more expensive production process of motion picture as compared to the look of a broadcast recorded from a video camera.
Production of works that originate on motion picture film typically costs three to five times as much as does the production of a video originated work. In addition, motion picture production often requires crew positions and film equipment that is much more expensive than broadcast video equipment.
The visually perceivable difference between the look of a broadcast made on a conventional video camera and the look of a broadcast made from motion picture film that has been transferred or converted to a video signal, can be important to the nature of the work being created and the medium in which it is intended to be broadcast, as well as the market it is trying to reach. This difference in appearance between these two methodologies is attributable in part to the differences between the way in which a conventional video camera captures and displays images as compared to the way in which a motion picture camera does the same.
A first difference between a video camera broadcast and a broadcast of motion picture film transferred or converted to a video signal is related to the way in which the video camera captures or freezes time as compared to how the motion picture camera captures or freezes time. A second difference in the broadcast outputs between these two methodologies is related to the contribution of film emulsion grain to the visual appearance of a motion picture film.
A conventional video camera captures action as a series of horizontal electronic scans of a photosensitive pick-up tube or a solid state, charged coupled device (CCD) type image sensor. The action in front of the lens of the video camera is output as a series of interlaced fields, or half frames. Two video fields are required to make up one complete video frame. The first video field consists of the odd numbered scan lines, while the second video field consists of the even numbered scan lines.
In the United States and other countries that use 60 Hz power, a broadcast field rate is approximately 60 fields per second, which yields a frame rate of about 30 frames per second.
A motion picture camera captures action as a series of still photographs by opening and closing the camera shutter at a predetermined rate. When viewed in rapid succession, these still images create the illusion of motion. In the United States and most other countries that have 60 Hz power, the standard camera and film projection speed is 24 frames per second. Those countries that have 50 Hz power use 25 frames per second as their standard film projection speed.
In order to view motion picture film on a conventional National Television Standards Committee (NTSC) video system, the film's 24 images per second must be converted to 60 video fields (or 30 video frames) per second. This film-to-video conversion process requires that 6 additional video frames be created each second from the 24 images per second motion picture film. Conventionally, these 6 extra video frames per second are created by scanning every other film image for three fields rather than two fields. This process of converting 24 images per second to 30 video frames per second is called "3-2 conversion." This process is well known in the broadcast industry as the methodology for converting motion picture film to video for broadcast.
With a conventional video camera, one second of time produces 60 independent video fields. By dividing each second into 60 separate video fields, the conventional video camera yields a smooth continuity of motion when broadcast.
For those countries and locations that do not use NTSC television systems, such as the United Kingdom and much of Europe, the 3-2 conversion process is not used. This is so because the motion picture film in these countries is photographed and projected at 25 frames per second, where each frame of film yields two video fields or one complete video frame. Occasionally, film for television broadcast is photographed at an increased rate of image capture of 30 frames per second. When this is done, the need for the 3-2 conversion for transferring the film to video is eliminated.
The 3-2 film-to-video conversion process creates a video sequence whereby motion within the scenes of the original motion picture film is displayed discontinuously. The viewer of such a broadcast may notice a "stepping" or "skipping" action to rapid motion within the scenes of the original film. In contrast, because of the way in which video cameras capture images, this stepping or skipping is largely undetected.
As noted above, the second major factor that contributes the look of motion picture film is the film media itself. The photochemistry of the light sensitive film emulsion that coats the film results in a granular image. The grain on film media appears as random patterns of similarly sized particles, localized into areas of similar exposure and density. The localized random patterns of particles creates a microscopic mosaic that produces a visual "texture" that is associated with the look of motion picture film.
Since each film image is photographed on and developed from a different piece of the film stock, the precise grain particle placement is uniquely different from frame to frame although the intensity of grain tends to be similar. As a result, even the photographing of a static scene will yield a constantly changing granularity on film media. The intensity of the grain effect can vary depending upon the film stock. Film stock with a higher sensitivity to light generally exhibits more visible grain than does film which is less sensitive to light.
Electronic noise of some level is generally produced by all video cameras. Some forms of random high frequency noise can appear as a type of granularity on video systems. However, this type of granularity is not of the same degree and nature, visually, as is the granularity created by the photochemistry of motion picture film. Random electronic noise has no spatial dependence and is generally only one scan line high.
The visual differences between broadcasts of works originally created on video cameras as compared to those created using motion picture film and motion picture cameras are well known to those skilled in the art. The principal causes of these differences as described above are used in connection with the present invention to help provide a video camera for real time simulation of the visual appearance of motion picture film that has been transferred or converted to a video signal, as well as a method for effecting such simulation. The desirability of producing movie quality broadcasts through a video medium has been long-felt, and there have been several attempts to achieve these and other related objectives, none of which employ the unique elements and steps of the present invention.
A method and apparatus for video image film simulation is described in U.S. Pat. No. 4,935,816 to Faber, whose description is incorporated by reference herein. Faber discloses a method and apparatus for receiving a conventional video signal from a prerecorded videotape or conventional video camera and processing the signal to provide the appearance of a motion picture film recorded image to be output directly for television broadcast or recording on videotape. Faber notes that video of recorded images does not contain grain and that noise or "snow" in a video system is typically undesirable. Faber states that extensive electronic filtering is employed to eliminate noise from electronic circuits and cameras, recorders and television sets for a clear picture.
Faber identifies three basic approaches for recording moving pictures; (1) photographic film exposed using a motion picture camera which is developed and printed to projection film, which may then be shown using a projector and screen; (2) videotaping where images are recorded directly on magnetic tape from a television or video camera; and (3) video cameras and videotape used for initial recording of moving picture images, followed by the breakdown of the recorded video into red, green and blue components which is then scanned onto photographic film, which is then processed and returned to videotape using the "telecine" process. Faber indicates that each of these approaches has certain technical limitations and undesirable costs associated with them.
Faber's solution to these shortcomings is to input a video signal from a video camera or prerecorded videotape and split it to provide a first real time signal for picture information and a second real time signal for synchronization and color burst information, and a first delayed signal and a second delayed signal. Faber provides clipped filter white noise with the picture portion of the first real time signal to simulate the "grain" of film, and then forms two interrelated fields that are routed through a third delay equal in length to the first delay. By sequentially repeating the interpolation of fields to be timed with predetermined delays, when processed the resultant video output comprises five field sets wherein each of the first four fields is an interpolation of a preceding and succeeding frame pair while the fifth field is a repeat of the third interpolated field.
Commercial efforts at creating film-like video cameras include a product known as the Ikegami EC 35 and a CEI/Panavision video camera. These two commercial products were introduced in the early 1980s, and both employed a similar concept of attempting to adapt a film lens to a modified hand-held tube type color camera. The external appearance of these two commercial products was much like a film camera, but the output pictures were generally on par with a high quality video camera and were not effective in simulating the look of a motion picture camera.
None of the above-described attempts at creating a video signal that can emulate the look of motion picture film has succeeded in creating a commercial and effective product, having the attributes of the present invention which are described hereafter.